Freeze, replanting and a later corn crop

When it comes to the aftermath of the Mid-South’s Easter freeze, throw out modeling predictions and conventional wisdom. In the freeze’s wake, there have been many surprises in the corn crop — usually unwelcome — for farmers and agriculture researchers alike.

“Southeast Missouri corn was devastated by the freeze,” says Al Wrather, Missouri Extension plant pathologist. “That became clear pretty early. But the damage in some wheat fields is still progressing nearly three weeks after the initial freeze. It’s difficult to explain how freeze injury is showing up so late after the event.”

In the past, “we’ve accepted that, following a freeze, a judgment on damage shouldn’t be made until four days have passed. Four days! This year proved that time period isn’t valid. It can take much longer.

“Consider that four days after the freeze, we saw corn that appeared on the verge of putting out new leaves. But the seed simply didn’t have the energy to push them out. And the four-day guideline is absolutely not valid when looking at wheat.”

Replanting in Arkansas is about 90 percent complete says Jason Kelley, Arkansas Extension corn specialist. Much more corn has been replanted in Arkansas than Kelley originally thought would be necessary. The numbers are still being tabulated, “but I believe close to a third of our acreage was replanted — 150,000 acres to 200,000 acres out of around 550,000 total corn acres. On a lot of corn acres, the growers had already side-dressed nitrogen and put atrazine out. Then the freeze hit and, ‘Oh, man, I’m locked into corn now. I’ve got to find some seed.’”

A formidable mistress

Rick Cartwright has never seen anything like the current freeze damage. “Hopefully this is a one-in-a-hundred-year event where everything comes together for bad,” says the Arkansas Extension plant pathologist.

“Mother Nature is a formidable mistress, and she isn’t one for much forgiveness. There was weather in March that favored planting a lot of acreage; there was a lot of emergence followed by a severe, late-spring freeze combined with a persistent cold spell that lasted several weeks. Talk about a head fake.”

The freeze predisposed corn “to things like Pythium, and some of the bacteria often called ‘soft rotters’” says Cartwright. “Normally, those things aren’t a big problem in corn. But adding in the plant injury factor and that ups their capacity for destruction.”

Tennessee had the best start for wheat and corn Melvin Newman had seen “in a long, long time. Now, the growing points in some of our corn are still alive. But the plants are sickly and lethargic and that’s a recipe for disease. Once all the energy from the seed is expended it can’t fight off problems and begin growing again.”

The later, replanted crop “unfortunately lowers the yield potential from the early-planted crop. Also, disease has a better chance in our corn — especially for gray leaf spot, which tends to limit production on susceptible varieties planted late. And we may have more of that corn because farmers didn’t get to replant varieties they would have preferred. To what extent that will play out, who knows? But the threat is there.”

Wrather agrees the freeze could have long-term repercussions. “Yields will probably be lower than farmers were expecting. That’s because this replanted corn won’t be emerging until, at earliest, the first part of May. That’s compared to a planting date of late March or early April.”

Increased disease pressures could also result.

“Among the diseases we’re concerned about are rust and gray leaf spot,” says Wrather. “The rust will be moving into the Bootheel from fields to the south. Any inoculum load — the spores that cause rust — could come in and impact our crop more than is normal.

“For example, a late-March planted crop that emerges the first of April may be halfway through the grain-fill process when rust arrives. Impact on yield could be minor.”

However, with May emergence, the corn crop could be at the beginning stages of grain fill when rust arrives this year. That means “impact on yield could be much more dramatic. Now, that’s all supposition but it isn’t wild speculation.”

On the other hand, Wrather says there could be some positives with a later crop. “Corn emerging in early May will likely produce kernels later in the summer when it’s a bit cooler than the early-planted crop. That could potentially mean fewer problems with aflatoxin. Regardless, producers need to water corn properly and stay on top of any insect problems.”

The days after

For seedling crops, the cold spell after Easter was almost as important as the freeze itself.

“It didn’t allow recovery,” says Cartwright. “That cold snap doomed the plants. If they could have recovered quickly and made food from the sun, the fields would have been in much better shape. But they just sat there. A professor of mine used to say, ‘When a plant sits in the cold nothing good will happen.’ And that’s true. Eventually something will get it.”

The northeast Arkansas farmers that Pioneer agronomist Roger Gipson is working with are nearly done replanting corn. “It’s strictly a guess, but between 50 and 60 percent of the corn from St. Francis County up to Clay County was replanted.

“After the freeze, there was an inch or so of green tissue left above the growing points. But the week following the freeze was abnormally cloudy, wet and cool and the plants stagnated.

“That was devastating, especially for the fields in the V-2 to V-4 growth stages. The seed reserves were used up and the plants ran out of gas.”

Meanwhile, the damaged tissue was still above the growing points and, “almost by the day, you could watch it moving lower and lower towards the growing points.”

After the freeze, “we needed 55-degree soil temperatures to get some growth on the corn,” says Kelley. “But we couldn’t get a break with the weather. Shortly after the freeze, the soil temp was 48 degrees.”

Another unusual occurrence: many corn fields in Mississippi’s central and south Delta are suffering from “twisted whorl syndrome.” Marked by bright yellow leaves and twisted whorls appearing in the top of individual plants, the problem is “closely correlated to the extreme temperature fluctuations our crop has endured during the past several weeks,” said Erick Larson in an alert to farmers. “Plants should grow out of this strange development relatively quickly. Most fields showing these symptoms range from V-5 to V-7 growth stage.

“Wrapped, twisted leaves are above freeze-damaged leaves (if present), indicating cool temperatures followed by recent warm, sunny weather are largely responsible for the problem. New leaves emerging from the whorl are initially quite yellow because they have been wrapped up and shaded longer than normal. These leaves should regain their green color within a few days.”

Water critical

Anytime a corn crop is pushed later into the season, “it increases the risk of problems: insects, stress, drought, heat and disease,” says Cartwright. “For both insects and certain foliar diseases, later planting allows them more generations. The later the crop, the more time insects and/or something like southern rust have to move and do damage.”

However, “the risk is truly unknown. We suspect it will be greater but that doesn’t hold true constantly. It is still April, after all.”

The late replanting is enough of a worry “that I’d probably budget a fungicide and insecticide, just in case. And I’d keep a closer eye on the crop.”

A later corn crop also means grain quality risks increase. “It’s imperative that corn growers don’t let the replanted corn have water stress,” says Cartwright. “That is absolutely critical for many reasons including the crop missing the early spring moisture. Once the corn begins growing it’s hard to keep up with. And now it’ll be later, hotter and drier so irrigation must be watched closely. Drought leads to many other problems.”

Bootheel producers “should plan for the possibility of spraying a foliar fungicide to protect against rust and other things,” says Wrather. “If needed, it should be applied when the tassel begins to emerge. I think fungicides on corn may be more important this year.”

Mid-South researchers are using the Easter freeze as an opportunity for study.

“I had some corn in test plots that sustained a lot of damage and uneven stands,” says Gene Stevens, Missouri Extension crop production specialist. “There were strips to compare nitrogen rates between sorghum and corn. After the freeze, I ditched that test and instead went with replant dates. At the end of the year, we’ll be able to tell what keeping the damaged plants versus replanting showed. We may not have the opportunity for another test like this in a long time. And I’m sure farmers would be fine with that.”